The present invention relates to aircraft capable of vertical take-off and landing and, more particularly, to aircraft capable of such maneuvers using split-torque face gear drives.
Aircraft designed to allow vertical and short take-off and landing, hover, full forward, and transitional flight have existed since about the middle of the twentieth century. These vehicles are often referred to as dual mode or V/STOL aircraft because of their vertical and/or short take-off and landing capabilities. There are four primary types of V/STOL vehicles: those having a single power plant for horizontal and vertical thrust; those having separate power plants for horizontal and vertical thrust; combined systems having separate power plants for horizontal and vertical thrust and a supplemental power plant to assist vertical propulsion; and augmented systems having an auxiliary vertical propulsion device powered by the primary propulsion device(s).
Numerous disadvantages of conventional V/STOL vehicles have kept them from more widespread and successful use. Many of these disadvantages stem from the fact that conventional designs are too complex and result in insufficient performance. The complexities associated with having multiple power plants, one or more to drive the vehicle horizontally and one or more to drive the vehicle vertically, are pronounced. An obvious shortcoming of a multiple power plant system is the weight added by and space required for the additional power plant(s). The aforementioned augmented systems require even more structure, which adds weight and takes space.
Conventional V/STOL systems using the same power plant for horizontal and vertical thrust have challenges related to the complexity of their designs. Examples of conventional single power plant designs include systems having deflector vanes in the downwash of horizontal thrusters and systems having tilting wings, thrusters, and/or power plant. The additional structure required by these systems adds excessive complexity and unwanted weight to the aircrafts.
Whether using a single power plant or multiple power plants for horizontal and vertical propulsion, conventional V/STOL systems are frequently overly complex, too heavy, and inefficient. In addition, there are many secondary weaknesses of conventional designs. For example, more complex systems generally cost more to manufacture and maintain. Also, because of added weight and, in many instances, power requirements, many conventional V/STOL vehicles have relatively short flight ranges and low fuel efficiencies. Low fuel efficiencies, in turn, result in low emissions performance, as more fuel is needed to carry the vehicle the same distance.
Other shortcomings of traditional devices include insufficient payload capacity. Poor payload capacity primarily results from a heavier base, or unloaded, vehicle. Payload characteristics also result from system design variables, such as spatial specifications. Many conventional V/STOL vehicles also exhibit poor maneuverability primarily due to their heaviness and underperforming steering and thrust systems. Finally, conventional V/STOL vehicles are frequently unreliable and sometimes experience stalling and part failure during operation. This unreliability is usually a result of the complexity, weight, and high power requirements of conventional V/STOL vehicles.